A frequency hopping method for localization system is aimed to overcome the degradation of location accuracy due to radio interference if there are some other radio devices using the same radio frequency as a localization system. A Packet Reception Rate (PRR) thresholding or a learning-based approach for the diagnostic test is proposed. In that, a PRR thresholding or a set of parameters trained by Hidden Markov Model (HMM) is used as a criterion to decide whether or not to hop. The proposed hopping mechanism provides an accurate and stable localization with a minimum delay.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A frequency hopping method for a localization system, comprising the steps of: (A) monitoring a packet reception rate of a beacon transmitter in the localization system within a tracking area, wherein the packet reception rate of the beacon transmitter is monitored only if the beacon transmitter receives a signal transmitted by a second beacon transmitter; (B) going to Step (C) if the packet reception rate of the beacon transmitter is below a threshold value; and (C) performing a frequency hopping to enter all beacon transmitters in the localization system into a stable frequency channel.
2. The frequency hopping method of claim 1 , wherein if the packet reception rate of the beacon transmitter is not less than the threshold value in Step (B), then the frequency hopping method returns to Step (A) to continue monitoring the beacon transmitter.
3. The frequency hopping method of claim 1 , wherein the threshold value is 35% to 55%.
4. The frequency hopping method of claim 1 , wherein the threshold value is 48%.
5. The frequency hopping method of claim 1 , wherein the beacon transmitter broadcasts a hopping request signal in Step (C), such that all beacon transmitters in the localization system perform a frequency hopping to enter into the stable frequency channel, and the frequency hopping method returns to Step (A) to continue monitoring the beacon transmitter.
6. A frequency hopping method for a localization system, comprising the steps of: (A) monitoring a packet reception rate of a beacon transmitter in the localization system within a tracking area (B) going to Step (C) if the beacon transmitter is interfered by a signal; and (C) performing a frequency hopping to enter all beacon transmitters in the localization system into a stable frequency channel; wherein step (A) comprises the steps of: (A0) entering into a link screening process, wherein the packet reception rate of the beacon transmitter is intercepted only if the beacon transmitter receives a signal transmitted by a second beacon transmitter; (A1) entering into an initialization stage, wherein the packet reception rate of the beacon transmitter is intercepted within the tracking area and used for training a HMM to obtain a set of parameters of the HMM and define a hopping observation range and a non-hopping observation range; (A2) entering into a diagnostic test stage, wherein a current packet reception rate of the beacon transmitter is intercepted, and the trained parameters of the HMM are used as a basis for estimating the HMM, so as to obtain a diagnostic test observation value; and Step (B) comprises the steps of: (B1) entering into a hopping determination stage, wherein if the diagnostic test observation value falls within the hopping observation range, the beacon transmitter will enter into Step (C).
7. The frequency hopping method of claim 6 , wherein if the diagnostic test observation value falls within the non-hopping observation range in Step (B1), the frequency hopping method will return to Step (A2) to continue monitoring the beacon transmitter.
8. The frequency hopping method of claim 6 , wherein the initialization stage intercepts the PRR of the beacon transmitter at a time period which includes the duration of signal interference and no signal interference.
9. The frequency hopping method of claim 6 , wherein the algorithm of training the HMM in the initialization stage is an EM algorithm.
10. The frequency hopping method of claim 6 , wherein the number of states of the hidden observation of the HMM in the initialization stage is equal to 2, and the range of hopping observation value indicates a greater hidden observation value, and the range of non-hopping observation value indicates a smaller hidden observation value comparatively.
11. The frequency hopping method of claim 6 , wherein the number of states of the hidden observation of the HMM in the initialization stage is equal to 3, the range of hopping observation value indicates the smallest hidden observation value, and the range of non-hopping observation values indicates the greatest and middle hidden observation values.
12. The frequency hopping method of claim 6 , wherein the diagnostic test observation value in the diagnostic test stage is a maximum output value obtained by estimating the HMM.
13. The frequency hopping method of claim 6 , wherein the algorithm of estimating the HMM in the diagnostic test stage is a forward algorithm.
14. The frequency hopping method of claim 6 , wherein the packet reception rate of the current beacon transmitter is retrieved once every 140 to 250 milliseconds in the diagnostic test stage.
15. The frequency hopping method of claim 6 , wherein the packet reception rate of the current beacon transmitter is retrieved once every 200 milliseconds in the diagnostic test stage.
16. The frequency hopping method of claim 6 , wherein if the beacon transmitter performs a frequency hopping in the hopping determination stage, a hopping request signal will be broadcasted, such that all beacon transmitters within the tracking area perform a frequency hopping to enter into the stable frequency channel, and the frequency hopping method returns to Step (A2) to continue monitoring the beacon transmitter.
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October 29, 2009
March 26, 2013
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